This invention relates to torque control apparatus and method for internal combustion engines in order to reduce variation in torque waveform, which is caused by an irregular combustion that occurs during an operation of the internal combustion engine.
The variation in torque of the internal combustion engine results in vibration and an abnormal noise of equipment, such as passenger cars, on which it is mounted. Therefore, various countermeasures have been taken with reard to the torque variation.
For example, in JP-A-61-171612, there is proposed an art in which an apparent (gross) torque of a crankshaft is made substantially even by applying a load torque to the crankshaft of an internal combustion engine in which the primary torque varies periodically. In this case, the load torque varies in synchronism with the primary torque variation of the crankshaft. A precondition for this torque unification technique is that the primary torque of the crankshaft varies periodically without fail. If the primary torque is varied irregularly for some reason, there is a possibility that the load torque applied to the crankshaft has such an adverse effect that the apparent torque exceeds the variation range of the primary torque. This phenomenon is not desirable because the vibration and/or abnormal noise mentioned above results.
Irregular combustion is considered as one reason for the irregular torque variation mentioned above. In internal combustion engines of late, the trend has been towards a twin-cam multi-valve engine with a high-speed type cam profile in order to produce high output and high engine speed. For this reason, in the low-speed region, particularly when the engine is in idling state, an irregular combustion tends to occur frequently. A possible cause of irregular combustion is considered to be a mixing of the fuel/air mixture and the exhaust gas when the intake valve and the exhaust valve are open simultaneously (valve overlap). Under this condition, even when the fuel/air mixture is ignited by the igniter, the flame does not propagate through the whole mixture in a cylinder and only local combustion takes place. This causes irregularity of the waveform of the gas torque, resulting in an irregular change in the primary torque of the crankshaft.